Extraction of oleiferous materials



Patented July 17, 1951 v UNITED STATES PATENT OFFICE EXTRACTION OFOLEIFEROUS MATERIALS Application April 23, 1947, Serial N 0. 7 43,285

10 Claims. (Cl. 260-4124) This invention relates to an improved methodfor recovering fatty materials, and similar high molecular weightmaterials, from the solid materials with which they are normallyassociated in nature. Such solid materials are referred to hereinafteras oleiierous solid. materials. Such oleiferous materials includevarious oil-bearing beans, seeds and nuts, designated generally as oilseeds, and including soybeans, cottonseed, linseed, peanuts, palm nutsand coconuts. Other oil-bearing solid materials of animal, vegetable andmarine origin also are included within the term oleiferous solidmaterials, such as animal tissue, including fish livers, vegetablefibers, nut shells, etc.

The invention relates particularly to an improved process of extractingoleiferous materials with relatively low-boiling solvents. Such solventsmay be defined as those whose critical temperature is not substantiallyhigher than 450 and preferably are lower than 325 F. Of these, thesolvents which are normally gaseous are preferred because of therelative ease with which they may be separated from the oil and theresidual solid material.

The low-boiling hydrocarbons represent .a desirable class of solventsbecause of their relative inertness and low cost. While the low-boilingolefin hydrocarbons may be employed they are less desirable than thelow-boiling paraffins such as ethane, propane, the butanes, the pentanesand the hexanes, from the point of view of .inertness. Of the paraffins,propane is preferred ordinarily because of the high degree of solubilityof the oils in that solvent and its relatively low critical temperaturewhich permits operating .in a temperature range not injurious to theoils. However, ethane or the butanes can be employed to almost as greatadvantage. While relatively pure hydrocarbons are preferred mixtures ofthem may be employed. For example, mixtures of ethane and propane ormixtures of butane and methane may be employed in the proportionssuitable to form solvents having the desired prop erties. While thenormally gaseous hydrocarbons are particularly advantageous for use .assolvents in the improved method other solvents having relatively lowcritical temperatures may be employed, such as ammonia, vdichlorodifluormethane, dimethyl ether, methyl fluoride and halogenated hydrocarbons ingeneral.

In accordance with the present invention the oleiferous solid materialsare contacted with the liquefied solvent at a temperature effective todissolve as :much of the oil as :is desired. or-

d-inarily the temperature is maintained at a .level effective to extractfrom the oleiierous solids the maximum quantity of the oil which can bedissolved in the amount of solvent available. Ordinarily also thesolvent is employed in a sufiic-iently great quantity to extract fromthe o-leif erous solids the maximum possible amount of oil.

The temperature employed for the extraction step depends upon thesolvent employed and the nature of the oil to be extracted from thesolid. While there is a temperature, or narrow range of temperatures, atwhich the solubility of the oil in the solvent is at a maximum, it ispossible ordinarily to extract substantially all the oil from the solidover a relatively wide range of temperatures, when employing asufficient quantity of solvent. For example, with propane the solventextraction step may be carried out at temperatures within the range offrom room temperature to approximately F.., to obtain :max-- imumextraction of oil, although higher and lower temperatures may beemployed if the propane: oil ratio is sufficiently high.

The olei-ferous solids, such as oil seeds, contain a substantialproportion of relatively fine nonioleagi-nou's solid material which isnot readily separable from the extract solution by :mere settling,particularly if the seeds are preliminarily flaked. Furthermore, inorder to enhance :the extraction ofoil the oil seeds may be subjected toa preliminary fine grinding treatment which increases the proportion offines. The bulk of the residual .non-oleaginous solid materials,consisting of relatively large particles, is readily separable trom theextract solution, as by .mere settling, but the suspended fines whichare not readily separable present a serious problem in connection withfiltration, particularly if it is desired to carry out filtration on ,acontinuous basis. In accordance with the improved process the extractsolution, after separating the solids which are readily separable, isheated to a temperature above the temperature, or range of temperatures,of maximum solubility, and to a temperature near :the criticaltemperature of the solvent, :to precipitate a'portion of the dissolvedoil as a .=se;oarate liquid phase. The formation of .the separate liquidphase occludes within the relatively heavy :droplets of oil the fineparticles of solid material carried in suspension in the extractsolution. The separate liquid "phase is readily settled out of theextractsolution by gravity, since the precipitated liquid phase issubstantially heavier than the extract solution, 'In :this mam In itssimplest embodiment the propane solution of the oil, after a preliminaryseparation of the readily separable solids, as by settling, is simplyheated to a temperature sufficiently high to precipitate enough of thedissolved oil to occlude the suspended finely divided solids. Thepropane solution may be heated to the precipitation temperature in theupper part of a zone in which the bulk of the solids are settled, or thepropane solution may be withdrawn from the preliminary separation zoneand heated before or after introduction into a separate settling zone.According to a preferred modification of the invention, which will bedescribed below in more detail, the propane solution is separated fromthe readily separable solid materials in a preliminary settling zone andpassed as a stream upwardly through a second settling zone in which thestream is heated through a range of temperatures above the temperatureof maximum solubility and near the critical temperature of the solventto effect precipitation of a separate liquid phase, containing thefines, which flows downwardly through the tower in countercurrentcontact with the upflowing propane solution.

The accompanying drawing presents diagrammatically an arrangement ofapparatus for carrying out the improved process, and the invention willbe described further by reference to the drawing, it being understoodthat the methods shown in the drawing are merely illustrative of theimproved process.

Referring to the drawing, oleiferous material, such as oil seeds, whichhas, preferably, been ground to a relatively fine state of subdivision,is supplied from hopper I through valve 2 to extractor 3. Extractor 3 isa relatively large vessel adapted to function on a batch basis, and isprovided with a bottom slurry outlet line 4 and an upper gas outlet line5. After the desired quantity of oleiferous material is introduced intoextractor 3, valve 2 is closed and a purging gas, such as nitrogen orflue gas, is introduced into outlet line 4 from supply line 6 which isprovided with a compressor 1 and a valve 8. Valve 9 in line 4 is keptclosed and valve I in line is kept open during the purging operationwhereby the purging gas flows upwardly through extractor 3 and the massof oleiferous material therein to purge the chamber of oxygen from theair introduced into the chamber along with the oleiferous material.After extractor 3 has been substantially completely purged of oxygen,valve I0 is closed, the flow of inert gas is stopped, and valve 8 isclosed. Optionally, the flow of inert gas into extractor 3 may becontinued to build up the pressure of that vessel to the level of anysuperatmospheric pressure desired during the extraction step.Alternatively, the source of supply of propane may be employed to buildup the pressure in extractor 3 to the necessary superatmospheric level.

Liquefied propane for use in the system is introduced through line I I,which is provided with a pump l2 and connects with a propane storagetank I3. From tank I3 liquefied propane is transferred to extractor 3through line I4 which is provided with a pump I5 and a valve I6, andconnects with line 4 between extractor 3 and valve 9. After extractor 3has been purged and valves 8 and iii are closed, liquefied propane ispumped into extractor 3 through lines I4 and 4 until the requiredquantity of propane for the extraction treatment of the oleiferousmaterial has been supplied to extractor 3. Thereafter the supply ofpropane is cut oil. Stirring means I! are provided in extractor 3 tointimately mix the oleiferous material and the liquefied propane andpromote extraction of oil by the propane.

The temperature in extractor 3 may be maintained at any desired level bysuitable control of the temperature of the propane. For this purposeheating or cooling means I8 may be provided in line I4. In a preferredmethod of operation of the improved process the temperature maintainedin extractor 3 is selected to produce maximum extraction of the oil bythe propane. For this purpose temperatures within the range ofatmospheric temperature to 140 F. may be employed, although higher orlower temperatures may be desired to produce special effects, such asthe partial extraction of the oil content of the oleiferone material.

After a suitable residence time in the extractor, the slurry of propanesolution and residual solid material is transferred to a verticallyelongated settling tank I9. Line 4 connects with tank I9 and is providedwith a pump 20. Valve 9 is opened and by means of pump 20 the slurry ispumped continuously into settling tank I9 at an intermediate point, asindicated in the drawing. Tank I9 is sufficiently large in relation tothe quantity of liquids charged thereto to facilitate the settling ofthe larger particles of the solid material from which the oil has beenlargely removed.

Tank I9 preferably is operated on a continuous basis by the provision ofone or more additional extractors in which a supply of the slurry ofpropane solution and solids is formed during the time slurry is beingtransferred from extractor 3 to settling tank I 9. Such an additional extractor is indicated at 3a., which is substantially identical inarrangement and operation with extractor 3, and in connection with whichsimilar parts are indicated by corresponding numerals with the subscripta.

The solid material separated by settling in tank l9 accumulates in thebottom of the tank and is withdrawn therefrom through line 2|. Propaneis supplied for washing the settled material at low points in tank I9through lines 22 and 23, which draw upon the supply of propane in linel4. The propane introduced through lines 22 and 23 removes propanesolution which is entrained by the solid material by washing anddilution and provides a liquid vehicle for the removal of the solidmaterials as a slurry through line 2|. The slurry is transferred to aseparating zone in vessel 24 with which line 2I connects at anintermediate point. A valve 25 is provided in line 2| to effectreduction of pressure on the slurry. This assists in the vaporization ofthe propane and provides a pressure diiferential for transferring theslurry.

The propane-oil solution, containing suspended finely divided solidmaterial not readily settled in tank [9, is withdrawn overhead throughline 26 which connects with tower 21, which may be designated as asecondary settling zone. In accordance with one modification, thepropane solution being transferred through line 255 is heated at 28 to asubstantially higher temperature to effect precipitation in line 26 of aseparate oil phase which oocludes the suspended solids. A pump 29 isprovided in line 28 to transfer the propane solution against the higherpressure which may be necessary at the elevated temperature ofprecipitation. In this modification the mixture of liquid phasesproduced as a result of heating at 28 is introduced at a high point intower 21 by connecting line '26 with tower 2'5 at a point near the top,indicated at In this modification tower 2'! functions as a verticallyelongated settling zone to permit complete separation of the liquidphases. Propane may be supplied to the bottom of tower 2'l from line 3!,which is provided with a pump 32 and connects with propane supply tank3. The propane introduced into the bottom of tower ill flows upwardlyand serves to scrub the oil phase which is flowing downwardly thereinand redissolve the more soluble portions thereof and leave a final lowerphase containing the fines. The propane stream combines with the propanesolution introduced into tower 21 from line 26 and the mixture passesoverhead from the tower through line Pressure on the solution isreleased at valve 3t and the resulting partially vaporized mixture isintroduced into a separator 35 in which vaporized propane is separatedand withdrawn overhead through line 36. Line 36 is provided with coolingmeans 3'! for condensing the propane and a pump 38 for transferring theliquefied propane into supply tank It, with which line 35 is connected.Heating means, not shown, may be supplied in separator 35 to assistvaporization of propane. The resulting oil, substantially completelyfree of suspended solids, is withdrawn from separator 35 through line39. This material may not be completely free of propane and may requirefurther treatment to remove such residual quantities of the solvent,such as steam stripping.

The oil phase separated from the propane solution by precipitation, andcontaining the fines, flows to the bottom of tower 27 and is withdrawnas a liquid stream through line flit. This material may be withdrawnentirely from the system, but preferably is recycled, at least in part,to the settling step of the extraction procedure to redissolve the oilin the propane solution and incorporate the fines in the residual solidswithdrawn from the bottom of settling tank it. For this purpose line 4!is provided to connect line 40 with tank l9 at a mid point thereof.Alternatively, the oil phase returned through line ll may be introducedat a relatively low point in tank l9, as by connection at A2, in orderto utilize the downwardly moving mass of solids to assist in trappingfines contained in the recycled oil. If tower 21 is employed toconcentrate the color bodies in the oil, according to a modificationdescribed below, a portion of the bottoms from tower 21 may be withdrawnfrom the system While another portion is recycled through line 4|. Inaccordance with another modification of the invention, the propanesolution from line 2'5 is introduced at a point near the bottom of tower21,, in the substantial absence of propane from any other source intower 2i. For this purpose line 43 is provided to connect line 2% withtower 21 at a low point. In this modification .the pro- ;panesolution isheated at most only partially at 28 and is heated to the final desiredhigh tem-- perature as it flows up the tower toward the exit at 33. Forheating the propane solution in tower 21 heating coils indicateddiagrammatically in the drawing are provided along the length of tower21, principally in the upper portion thereof, to heat the propanesolution gradually to the final desired high temperature. In this mannerprecipitation of the lower phase occurs all along the length of the pathin which the stream is heated whereby the occlusion of fines in thedroplets formed by precipitation is enhanced. The precipitate formed intower 2! flows down the tower and is subjected to countercurrent contactwith the upflowing propane solution. By this means the oil isfractionated to a greater degree and the concentration of less solublecomponents in the lower phase is increased. To enhance this effect thepropane solution may be introduced at a point somewhat removed from thebottom of tower 2! as through line 44, while additional propane isintroduced at the bottom through line 3 l. Additional propane serves toscrub the lower phase for the recovery of more soluble componentsthereof prior to withdrawal of the lower phase from tower 27 throughline ltl. To enhance the scrubbing action of the additional propane thepropane solution may be introduced at a point near the middle of tower27, as through line 45.

To intensify the rectification of the tower, produced by theprecipitation of the lower phase, and produce closer fractionation ofthe oil, a portion of the extract oil recovered overhead at 35 may bereturned through line t6 to the upper portion of tower 21. Tower 27 maybe provided with trays or packing to enhance contact of the liquidphases.

The proportion of the oil which is precipitated from the propanesolution to effect removal of fines may vary from 1 to 20 percent, orhigher. The oil thus precipitated is not lost from the product, as itmay be recycled to the separation zone through line ll and redissolvedin the propane phase. If it is desired to utilize tower 27 as a meansfor concentrating color bodies of the oil in a small bottoms fractionwhich is to be withdrawn from the system, it is preferable to heat thepropane phase to a final high temperature in tower 2? which precipitatesa substantially large pro ortion of the oil, which is then subjected toscrubbing treatment with additional propane from line 3| in the bottomof tower 21 to reduce the volume or" the lower phase, by redissolvingoil, to the proportion of the oil charge which it is desired to removefrom the system as the color body fraction. Ordinarily the temperaturesto which the propane solution is to be heated are all within the rangeof -200 F.

The solids are withdrawn from separator '24 through line 4'! in arelatively dry condition by any suitable means, such as star feeder. Thesolids thus withdrawn are then subjected to further treatment, as bysteam, for the removal of propane therefrom. To assist the removal ofpropane in separator M suitable heating means, such as a heating coil,not shown, may be provided in separator 24. The propane withdrawnoverhead in separator 2 t transferred through line 38 to line 35 forpassage back to propane storage at 13. A compress-or a9 is provided inline 48 to recompress the propane to the pressure of line 36.

Instead of operating the extraction zones on a batch basis as isillustrated in the drawing, it

is within the scope of the invention to contin-- uously mix the solventand solids in a continuous extraction zone and continuously transfer theresulting mixture of propane solution and solids to settling tank 19. Inthis operation some of the oil may be extracted in tank 19, particularlyif additional propane is introduced through lines 22 and 23.

In the foregoing description, the final separation of finely dividednon-oleaginous solids by precipitation of a separate liquid phasefollows a preliminary partial separation of the readily separableportion consisting of the larger particles of the solid material whichhas been subjected to extraction treatment. For an example of such apreliminary separation reference has been made to simple settling ofsuch readily separable solid materials, and in the detailed descriptionof the invention, as illustrated in the drawing, this preliminaryseparation step has been provided for by passing the slurry from theextraction zone to an enlarged settling vessel shown in the drawing atl9. It will be understood, however, that the invention is not limited toan operation in which the preliminary separation is effected bysettling, since other methods may be employed to separate the readilyseparable solids prior to the final separation step. For example,instead of a settling step the slurry from the extraction zone may bepassed to a filtration step in which the filtering medium is relativelycoarse. The coarseness of the filtering surface prevents clogging andgreatly simplifies the operation, but permits the passage of relativelyfine solid materials, which are separated by precipitation of a separateliquid phase in a subsequent zone. In accordance with another method ofeffecting preliminary separation of the readily separable materials, theslurry from the extraction zone may be passed to a centrifugalseparation apparatus on which the duty would be quite low, since itwould not be necessary to separate the finest portion of the solidmaterial. It will be understood, therefore, that in the foregoingdescription and in the following claims references to the preliminaryseparation of readily separable solids are not limited in their specificapplication to the settling method shown in the drawing.

The separate liquid phase which is formed by heating the extract phaseis readily separated by settling, as indicated above. However, othermeans for efiecting such separation, such as a centrifuge, are withinthe scope of the invention.

As stated above, the temperature at which the extraction step is carriedout is maintained at the level at which the desired proportion of theoil content of the oleiferous material is dissolved in the solvent. Itis within the scope of the invention to maintain the temperature ofextraction at a level substantially above the temperature of maximumsolubility whereby only a portion of the oil contained in the oleiferousmaterial is dissolved in the solvent. This permits selective extractionof desired portions of the oil while leaving with the solid residue aportion of the oil which it is not desired to include in the extract.This involves conducting the extraction at temperatures substantiallyabove the temperature levels employed in previous extraction processesand at temperatures not far below the critical temperature of thesolvent. For example, when it is desired to extract only a portion ofthe oil in accordance with this modification the minimum temperature inthe extraction zone should not be more than about 70 F. below thecritical temperature of the solvent. When employing propane as thesolvent in accordance modification the extraction temperature should notbe lower than about 140 F. Relatively high temperatures above this levelare employed to extract smaller portions of the oil content of theoleiferous solids.

In carrying out the process according to the:

modification in which only a portion of the oil is extracted from theoleiferous solid the latter may be subjected to a plurality ofsuccessive treatments at decreasing temperature levels to extract apluralit of separate fractions of the.

substantially above 140 F., to extract a portion of the oil which isunusually light in color and free from color bodies. centrated the freefatty acids, the unsaponifiable portion of the oil or fat, and anyoil-soluble vitamins present in the oil. In a second partial extractionof the oleiferous material at a somewhat lower temperature another oilfraction is obtained which is substantially free from color bodies andwhich is different in composition from the first oil fraction in beingrelatively free from fatty acids and unsaponifiable material. If thesecond treatment is carried out at a temperature substantially above thetemperature of maximum solubility the second oil fraction also will berelatively free from color bodies. By carrying out repeated treatmentsat successively lower temperatures all the desired materials are finallyremoved, leaving only undesirable extractable materials with the solidportion of the oleiferous material. The products of such successiveextraction steps represent semi-refined, or fully refined, fractionswhich, because of the method of production, do not require subsequentrefining to the extent required by oils recovered by previous methods.

In carrying out successive extraction treatments by the methodillustrated in the drawing the first treatment would be at substantiallyelevated temperature whereby the solids settled out in tank 19 wouldcontain a substantial proportion of unextracted material. The slurry ofsuch solids and propane withdrawn from tank I9 through line 2| would notbe passed to a zone of lower pressure as illustrated in the drawing,

but would be transferred by means of a suitable pump to a secondextraction step generally similar to that illustrated in the drawing forcontact with an additional supply of propane at a lower temperature.

I claim:

1. A method for recovering oil from solid oleiferous material containingoleaginous material associated with non-oleaginous material whichcomprises intimately contacting said oleiferous material with a solventfor the oil content thereof to form a slurry of solids in extractsolution, said solvent having a critical temperature not "substantiallyhigher than 450 degrees Fahrenheit, separating readily separable coarsersolid particles from said slurry leaving a suspension of solid fines inthe extract solution, heating said while maintaining said suspensionunder a pressure sufficient to prevent substantial vaporize- In thisfraction are con tion of said solvent, and separating saidfinescontaining oil phase from the remaining extract solution.

2. A method for recovering oil from solid oleiferous materia] containingoleaginous material associated with non-oleaginous material whichcomprises intimately contacting said oleiferous material with a solventfor the oil content thereof to form a slurry of solids in extractsolution, said solvent having a critical temperature below 325 degreesFahrenheit, separating readily separable coarser solid particles fromsaid slurry leaving a suspension of solid fines in the extract solution,heating said suspension to a temperature above the temperature ofmaximum oil solubility and near the critical temperature of said solventto precipitate an oil phase heavier than said extract solution andcontaining said solid fines in occlusion while maintaining saidsuspension under a pressure sufficient to prevent substantialvaporization of said solvent, and separating said fines-containing oilphase from the remaining extract solution.

3. A method according to claim 1 in which said solvent comprises aliquefied normally gaseous material.

4. A method according to claim 1 in which said solvent comprises aliquefied normally gaseous hydrocarbon.

5. A method according to claim 1 in which said oleiferous material iscontacted with said solvent at a temperature efiective to dissolve amaxi mum amount of said oleaginous material in said solvent.

6. A method for recovering oil from solid oleiferous material containingoleaginous material associated with non-oleaginous material whichcomprises intimately contacting said oleiferous material with a solventfor the oil content thereof to form a slurry of solids in extract solu-.5;

tion, said solid having a critical temperature not substantially higherthan 450 degrees Fahrenheit, separating a readily separable coarserportion of the solids from said slurry in a separation zone leaving asuspension of solid fines in the extract solution, heating saidsuspension to a temperature above the temperature of maximum oilsolubility and near the critical temperature of said solvent toprecipitate an oil phase heavier than said extract solution andcontaining said solid fines in occlusion while maintaining saidsuspension under a pressure sufiicient to prevent substantialvaporization of said solvent, separating said fines-containing oil phasefrom the remaining extract solution, and returning the saidfines-containing oil phase to said separation zone.

7. A method for recovering oil from solid oleiferous material containingoleaginous material associated with non-oleaginous material whichcomprises intimately contacting said oleiferous material with a solventfor the oil content thereof to form a slurry of solids in extractsolution, said solvent having a critical temperature not substantiallyhigher than 450 degrees Fahrenheit, separating readily separable coarsersolid particles from said slurry by settling leaving a suspension ofsolid fines in the extract solution, heating said suspension to atemperature above the temperature of maximum oil solubility and near thecritical temperature of said solvent to precipitate an oil phase heavierthan said extract solution and containing said solid fines in occlusionWhile maintaining said suspension under a pressure sufiicient to preventsubstantial vaporization of said solvent, and separating saidfines-containing oil phase from the remaining extract solution.

3. A method according to claim '7 and the step of returning saidfines-containing oil phase to the zone of settling of said readilyseparable solids.

9. In the recovery of oil from oil seeds by extraction with a solventfor the oil content therehaving a critical temperature not substantiallyier than 450 degrees Fahrenheit, the improved method which comprisescrushing the oil seeds, intimately contacting the crushed seeds withsaid solvent under liquefying pressure to form a slurry of solids inextract solution, separating readily separable coarser seed particlesfrom said slurry leaving a suspension of solid fines in the extractsolution, adjusting the temperature of said suspension to the range nearthe critical temperature in which the solubility of oil in the solventdecreases with increasing temperature to precipitate a relatively heavyraiiinate phase in sufficient quantity to carry down said solid finesand separately withdrawing said extract solution substantially free ofsolid fines.

16. In the recovery of oil from seeds by extraction with a solvent forthe oil content thereof having a critical temperature not substantiallyhigher than 450 degrees Fahrenheit, the improved method which comprisesintimately contacting said seeds in finely divided form with saidsolvent under liqueiying pressure to form a slurry of solids in extractsolution, separating readily separable coarser seed particles from saidslurry leaving a suspension of solid fines in the extract solution,continuously introducing said suspension into a vertically extendedfractionation zone through a mixture inlet located above a solvent inletand a rafiinate phase outlet and below an extract phase outlet,countercurrently contacting said suspension with additional quantitiesof said solvent introduced through said solvent inlet, maintaining agradient of temperature increasing with elevation within saidfractionation zone in the region between said mixture inlet and saidextract phase outlet, said temperature gradient being in the range nearthe critical temperature in which solubility of oil in said solventdecreases with increasing temperature, adjusting said temperaturegradient to precipitate from said suspension a relatively heavyrafiinate phase in suflicient quantity to carry carry down said solidfines, and separately withdrawing extract and ramnate phases from saidextract and raflinate phase outlets respectively.

JOHN T. DICKINSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,849,886 Rosenthal Mar. 15, 19322,118,454 Schaafsma May 24, 1938 2,152,667 Rosenthal Apr. 4, 19392,254,245 Rosenthal Sept. 2, 1941 2,270,674 Pilat et al Jan. 20, 19422,281,865 Van Dijck May 5, 1942 2,329,889 Ewing Sept. 21, 1943

